1. Technical Field of the Invention
The present invention relates to liquid crystal devices, color filter substrates, methods for manufacturing liquid crystal devices, and methods for manufacturing color filter substrates.
2. Description of the Related Art
In general, in a liquid crystal device having a liquid crystal panel in which a pair of substrates composed of a glass or the like holds liquid crystal therebetween, a color filter substrate may be used in some cases in order to perform color display. In this color filter substrate, color layers (for example, R (red), G (green), B (blue), and BM (black: black matrix or black mask)) for constituting a filter portion of the color filter are formed on a surface of a transparent substrate such as a glass. These color layers are formed of a resin containing a coloring agent, such as a pigment or a dye.
In the color filter, a surface protective layer composed of a transparent resin or the like is generally formed on the color layers. This surface protective layer is formed for preventing infiltration of a chemical solution when another layer (such as a transparent electrode pattern) is further formed on the color filter and, in addition, is formed so as to ensure the flatness of the surface of the color filter.
On the surface of the color filter, transparent electrodes composed of a transparent conductive material such as ITO (Indium Tin Oxide) may be formed in some cases. However, in general, since the adhesion between the surface protective layer and the transparent electrodes described above is insufficient, when the transparent electrodes are formed directly on the color filter, there has been a problem in that the pattern accuracy of the electrode pattern cannot be ensured. Accordingly, heretofore, an insulating film (an intermediate layer) composed of SiO2 is formed by sputtering or the like on the surface of the surface protective layer formed on the color filter, and the transparent electrodes are formed on this insulating film.
When the transparent electrodes are formed on the insulating film described above, since the transparent electrodes are formed by patterning a transparent conductive film formed by sputtering or the like, a resist pattern on the transparent conductive layer must be developed by using an alkaline solution such as an aqueous solution containing potassium hydroxide, and in addition, after the transparent electrodes are formed by patterning, the remaining resist pattern on the electrode pattern must be removed by an alkaline solution.
However, since an insulating film composed of SiO2 has poor resistance against the alkaline solution described above, the insulating film is adversely influenced by this chemical treatment, for example, part of the insulating film is dissolved by the alkaline solution while the transparent electrodes are formed by patterning, and as a result, the insulating film may be separated from the color filter in some cases.
In addition, when an insulating film composed of SiO2 is formed by using a sputtering apparatus, SiO2 adhered to the inside of the apparatus is spread in the powdered form, and as a result, there is a problem in that the environment is contaminated. The reason for this is that since SiO2 has a coefficient of thermal expansion significantly different from those of metal constituent members used inside the apparatus and also has the property of easily absorbing the moisture in air, the SiO2 adhered to the inside of the apparatus is easily separated from the inside surface of the apparatus after sputtering is completed. In addition, when a SiO2 film is formed by sputtering, an abnormal discharge is likely to occur on the target due to a low dielectric constant thereof, and hence, there is also a problem in that it is difficult to obtain stable film-forming conditions.
Furthermore, compared to the transparent electrode described above generally having a high refractive index of approximately 1.8 to 1.9, since the insulating film composed of SiO2 has a low refractive index (n=1.455), the light transmittance is decreased due to the occurrence of light reflection or interference at the interface between the insulating film and the transparent electrode, and as a result, there has been a problem in that the brightness of display is decreased.
Accordingly, the present invention was made to solve the problems described above, and an object of the present invention is, in a color filter substrate or a liquid crystal device having a conductive film formed on the color filter, to provide a structure which can suppress the problems caused by an insulating film provided between the color filter and the conductive film.
A liquid crystal device of the present invention comprises: a first substrate; a second substrate disposed so as to oppose the first substrate; a color layer provided on the first substrate; an insulating film provided on the color layer and comprising at least one of Ta2O5, ZrO2, and TiO2 as a primary component; and a conductive film having the property of transmitting light provided on the insulating film.
Since Ta2O5, ZrO2, and TiO2 each has a refractive index higher than that of SiO2, the difference in refractive index from the transparent conductive layer can be decreased, and the optical loss at a laminated portion formed of the transparent conductive layer and the insulating film can be decreased. In particular, the refractive index of the metal oxide described above which is formed by a vapor phase method can also be controlled or adjusted by the film-forming conditions therefor. In addition, since the insulating film used in the present invention is unlikely to produce particles compared to that composed of SiO2, the degree of contamination in the environment in the manufacturing process can be decreased.
In addition, since both Ta2O5 and ZrO2 formed by a vapor phase method have sufficient corrosion resistance against an alkaline solution, the separation thereof is unlikely to occur when an alkaline solution is used for patterning the transparent conductive layer. That is, the insulating film preferably comprises at least one of Ta2O5 and ZrO2 so as to have alkali resistance.
When an optional wavelength in the visible wavelength region is represented by xcex, it is preferable that the sum of the optical thickness of the insulating film and the optical thickness of the conductive film of the present invention be substantially equal to the product of xcex/2 and a natural number. In the case described above, at the surface of the insulating film at the color filter side and at the surface of the conductive film at the side opposite to the color filter, reflectance of a visible light can be decreased, and as a result, the light transmittance can be increased.
The optical thickness can be represented by nxc2x7d (n is the refractive index of the laminated portion, and d is the total thickness of the insulating film and the conductive film) when the insulating film and the conductive film have substantially the same refractive index, and when the refractive index of the insulating film and the refractive index of the conductive film substantially differ from each other, the optical thickness can be represented by n1xc2x7d1+n2xc2x7d2 (n1 is the refractive index of the insulating film, d1 is the thickness of the insulating film, n2 is the refractive index of the conductive film, and d2 is the thickness of the conductive film). In addition, the visible wavelength region described above is a region in which the wavelength is in the range of from 380 nm to 780 nm. As a typical wavelength in the visible wavelength region, xcex described above is preferably 550 nm.
In the present invention, it is preferable that a transparent resin film be further provided between the color layer and the insulating film. This transparent resin film (the surface protective layer described later) is generally formed so as to protect the color layer and, in addition, is formed so as to planarize the surface of the color filter. By forming this resin film, the insulating film is further planarized.
In the present invention, there may be a case in which a reflective film is further provided between the color layer and the first substrate. In a reflective liquid crystal device or in a transflective liquid crystal device, by providing the reflective film, reflective display using ambient light can be realized. As a material for the reflective film, aluminum, an aluminum alloy, chromium, a chromium alloy, silver, a silver alloy, and the like can be generally used. In the case described above, by providing opening portions in the reflective film described above, since light is allowed to pass through these opening portions, a transflective liquid crystal device can be formed.
In the present invention, there may be a case in which an underlying layer composed of a material substantially identical to that for the insulating film described above is further provided on the second substrate described above, and an active element is further provided on the underlying layer described above. The underlying layer composed of the material substantially identical to that for the insulating film can improve the adhesion of the second substrate with the active element, a conductive film forming wires and electrodes electrically connected to the active element, and the like. As the active element, for example, a TFD (Thin Film Diode) may be mentioned.
In addition, another liquid crystal device of the present invention comprises: a first substrate; a second substrate disposed so as to oppose the first substrate; a color layer provided on the first substrate; an insulating film provided on the color layer and comprising Ta2O5 as a primary component; and a conductive film having the property of transmitting light provided on the insulating film. Since the insulating film comprising Ta2O5 as a primary component has high corrosion resistance against an alkaline solution, the separation thereof is unlikely to occur even when the transparent conductive layer is patterned by using an alkaline solution. In addition, since the insulating film described above has a high refractive index compared to that composed of SiO2, the difference in refractive index from the transparent conductive layer can be decreased, whereby the optical loss at the laminated portion formed of the transparent conductive layer and the insulating film can be decreased. Furthermore, since the insulating film described above is unlikely to produce particles compared to that composed of SiO2, the degree of contamination in the environment in the manufacturing process can be decreased.
In the liquid crystal device described above, the insulating film preferably comprises at least one of ZrO2, TiO2, and SiO2 as a component. In addition to Ta2O5, when at least one of ZrO2, TiO2, and SiO2 is contained as a primary component, the refractive index, the dielectric constant, and the like can be adjusted, and hence, the degree of freedom of optical and electrical design for the apparatus can be ensured.
In particular, concerning the transparent conductive layer, since there are essentially limitations of the thickness and the composition in order to obtain desired electrical properties (the absolute value of resistance, resistivity, and the like), it has been difficult to obtain a desired thickness and a refractive index (which varies in accordance with the composition or film-forming conditions) in terms of optical properties, and hence, the degree of freedom of optical design has been limited. However, when the insulating film is formed so that the refractive index thereof is close to that of the transparent conductive layer compared to that obtained in the past, the insulating film and the transparent conductive film can be regarded as materials having optical properties similar to each other (for example, an integrated material). As a result, when the thickness, the refractive index, and the like of the insulating film are adequately designed, for example, the laminated portion formed of the insulating film and the transparent conductive layer can be regarded as an integrated optical element, whereby the degree of freedom of optical design can be increased. In particular, it is preferable that the refractive index of the insulating film and the refractive index of the transparent conductive film be substantially equal to each other.
In addition, still another liquid crystal device of the present invention comprises an insulating film comprising at least one of Ta2O5, ZrO2, and TiO2 as a primary component, and a conductive film having the property of transmitting light provided on the insulating film.
Furthermore, another liquid crystal device of the present invention comprises: a first substrate; a second substrate disposed so as to oppose the first substrate; a color layer provided on the first substrate; an insulating film provided on the color layer, having the property of transmitting light, a refractive index of 1.6 to 2.0 in the visible wavelength region, and a thickness of 10 nm to 100 nm; and a conductive film provided on the insulating film, having the property of transmitting light, a refractive index of 1.8 to 1.9 in the visible wavelength region, and a thickness of 100 nm to 300 nm.
In the liquid crystal device described above, the difference in refractive index between the insulating film and the conductive film can be decreased compared to that obtained in the past, and in addition, since the sum of the optical thicknesses of the insulating film and the conductive film is approximately one time to two times the visible wavelength xcex, the reflection at the interface can be reduced, whereby the optical loss caused by the laminated portion formed of the insulating film and the transparent conductive layer can be reduced.
In addition, still another liquid crystal device of the present invention comprises: an insulating film having a refractive index of 1.6 to 2.0 in the visible wavelength region and a thickness of 10 nm to 100 nm; and a conductive film provided on the insulating film, having the property of transmitting light, a refractive index of 1.8 to 1.9 in the visible wavelength region, and a thickness of 100 nm to 300 nm.
Next, a color filter substrate of the present invention comprises: a substrate; a color layer provided on the substrate; an insulating film provided on the color layer and comprising at least one of Ta2O5, ZrO2, and TiO2 as a primary component; and a conductive film having the property of transmitting light provided on the insulating film.
In addition, another color filter substrate of the present invention comprises: a substrate; a color layer provided on the substrate; an insulating film provided on the color layer and comprising Ta2O5 as a primary component; and a conductive film having the property of transmitting light provided on the insulating film.
Furthermore, still another color filter substrate of the present invention comprises: a substrate; a color layer provided on the substrate; an insulating film provided on the color layer, having the property of transmitting light, a refractive index of 1.6 to 2.0 in the visible wavelength region, and a thickness of 10 nm to 100 nm; and a conductive film provided on the insulating film, having the property of transmitting light, a refractive index of 1.8 to 1.9, and a thickness of 100 nm to 300 nm.
Next, a method for manufacturing a liquid crystal device of the present invention comprises: a step of forming a color layer on a first substrate; a step of forming an insulating film on the color layer, the insulating film comprising at least one of Ta2O5, ZrO2, and TiO2 as a primary component; a step of forming a conductive film having the property of transmitting light on the insulating film; and a step of patterning the conductive film by using an alkaline solution. Since the insulating film described above has high alkali resistance, even when the conductive film is patterned by using an alkaline solution, degradation of the film quality and separation of the film are unlikely to occur, and in addition, damage that might be done on the color layer formed thereunder can also be prevented.
In the method described above, the insulating film and the conductive film are preferably formed so that when an optional wavelength in the visible wavelength region is represented by xcex, the sum of the optical thickness of the insulating film and the optical thickness of the conductive film is substantially equal to the product of xcex/2 and a natural number.
In addition, the method described above preferably further comprises a step of forming a transparent resin film on the color layer.
Furthermore, the method described above preferably further comprises a step of forming a reflective film on the first substrate. In this step, when opening portions are provided in the reflective film, a transflective liquid crystal device can be formed.
In addition, the method described above preferably further comprises a step of forming an underlying layer composed of a material substantially identical to that for the insulating film on the second substrate, and a step of forming an active element on the underlying layer. By forming the underlying layer composed of the material substantially identical to that for the insulating film, the adhesion of the substrate with the active element, and wires and electrodes connected thereto, can be improved. In addition, since the insulating film formed on the first substrate and the underlying layer formed on the second substrate are composed of substantially the same material, the process control can be easily performed, and the manufacturing cost can also be reduced. Furthermore, the insulating film and the underlying layer may be simultaneously formed on the first substrate and the second substrate, respectively.
In particular, by forming a metal conductive layer primarily composed of Ta on the second substrate with an insulating film comprising Ta2O5 as a primary component provided therebetween, the adhesion between the metal conductive layer and the substrate can be increased, and in addition, diffusion of the impurities from the substrate can be prevented. As described above, when the layer comprising Ta2O5 as a primary component is formed on each of the pair of substrates forming the liquid crystal device, since the film-forming apparatus can be interchangeably used, and the insulating film and the insulating layer can be simultaneously formed, flexibility of the manufacturing process can be increased, and in addition, the number of the manufacturing steps can also be decreased.
In the present invention, the insulating film described above is preferably formed by vapor phase film-forming means. The metal oxide formed by vapor phase film-forming means, such as PVD (physical vapor deposition) or CVD (chemical vapor deposition), is stable at a heating temperature (approximately 200 to 300xc2x0 C.) for forming the transparent conductive layer, has dense film quality, and has superior alkali resistance. In particular, PVD (a physical vapor deposition method or a physical deposition method), such as a deposition method, a sputtering method, or an ion plating method, is preferably used for film formation.
In addition, another method for manufacturing a liquid crystal device of the present invention comprises: a step of forming a color layer on a substrate; a step of forming an insulating film on the color layer, the insulating film comprising Ta2O5 as a primary component and at least one of ZrO2, TiO2, and SiO2 as a component; a step of forming a conductive film having the property of transmitting light on the insulating film; and a step of patterning the conductive film by using an alkaline solution.
Furthermore, still another method for manufacturing a liquid crystal device of the present invention comprises: a step of forming a color layer on a substrate; a step of forming an insulating film on the color layer, the insulating film having the property of transmitting light, a refractive index of 1.6 to 2.0 in the visible wavelength region, and a thickness of 10 nm to 100 nm; and a step of forming a conductive film on the insulating film, the conductive film having the property of transmitting light, a refractive index of 1.8 to 1.9 in the visible wavelength region, and a thickness of 100 nm to 300 nm.
Next, a method for manufacturing a color filter substrate according to the present invention comprises: a step of forming a color layer on a substrate; a step of forming an insulating film on the color layer, the insulating film comprising at least one of Ta2O5, ZrO2, and TiO2 as a primary component; a step of forming a conductive film having the property of transmitting light on the insulating film; and a step of patterning the conductive film by using an alkaline solution.
In addition, another method for manufacturing a color filter substrate of the present invention comprises: a step of forming a color layer on a substrate; a step of forming an insulating film on the color layer, the insulating film having the property of transmitting light, a refractive index of 1.6 to 2.0 in the visible wavelength region, and a thickness of 10 nm to 100 nm; and a step of forming a conductive film on the insulating film, the conductive film having the property of transmitting light, a refractive index of 1.8 to 1.9 in the visible wavelength region, and a thickness of 100 nm to 300 nm.
In the methods described above according to the present invention, it is preferable that the insulating film and the conductive film be successively formed in the same apparatus. In the case in which the insulating film is formed by vapor phase film-forming means, when the insulating film is formed in the same apparatus as that for forming the transparent conductive film, and successively, the conductive film is formed, the cleanness at the interface between the insulating film and the transparent conductive layer can be ensured, whereby the adhesion between the two layers can be improved, and in addition, the optical and the electrical properties can be improved by virtue of the decrease in contamination at the interface. In the case described above, it is particularly preferable that the insulating film and the conductive film be successively formed by a sputtering method in the same sputtering apparatus.
In addition, in the step of patterning the conductive film described above, patterning treatment is preferably performed on the conductive film described above by etching using an alkaline solution. In patterning treatment, for example, there may be a case in which a resist pattern is formed by development using an alkaline solution, and the transparent conductive film is then patterned by using this resist pattern. In addition, after the transparent conductive layer is patterned, an alkaline solution is also used for removing the remaining resist pattern. In the case described above, since the insulating film is formed of a material having high alkali resistance, the insulating film is prevented from being corroded by the alkaline solution, and hence, a problem in that the insulating film is separated from the color filter or the like can be avoided.
The color filter substrate described above can be applied to various liquid crystal devices: which use various display principles, such as a TN or an STN type; which are provided with various panel structures, such as an active matrix type, a passive matrix type, or a segment type; and which are provided with various structures, such as a transmissive type, a reflective type, or a transflective type. In addition to the liquid crystal devices described above, the color filter substrate can also be used as color filter portions of various devices, such as a display portion of a CRT (a cathode ray tube) or a light-receiving surface portion of an imaging tube, as long as the devices are each provided with a color filter and a transparent conductive layer.